I really don't get this. Why do people strive to get richer??

I've chose startup grind instead of super rich Facebook jobs 3 years ago and am still living like a student and see no need to own a lot of things. Am I that "special", to me it seems completely logical to sacrifice short term rewards to be in for the long run, delayed gratification and everything.

Once I've made it, I don't see either, why I would burn myself just to have e.g. $20M instead of $10M. wtf?